The PBO and Sign files in the archive need to be extracted into your ArmA/Addons folder.
However the mod folder method is the better solution.
Copy the following URL into your browser to view a Mod Folder Tutorial : http://tinyurl.com/armamodfolder

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CREDITS AND THANKS:
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Additional resources:
GoogleEarth

One or more textures on this map have been created with images from CGTextures.com. These images may not be redistributed by default. Please visit www.cgtextures.com for more information.

This readme has been made by using the ArmedAssault.info Readme Generator.

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DISCLAIMER:
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This addon is not related in any way to Bohemia Interactive Studios or Bohemia Interactive Simulations. You may ONLY use this addon in Arma2: Combined Operations, Arma2 and Arma2 Operation Arrowhead.

I take no responsibility for (im)possible damage to your game/system that may be caused
by installation of this Addon. This Addon is also prohibited to be used in any commercial product.